Building block



FIG. 1 is a top perspective view of a building block;

FIG. 2 is a bottom perspective view of a building block;

FIG. 3 is a top view of a building block;

FIG. 4 is a bottom view of a building block;

FIG. 5 is a side view of a building block;

FIG. 6 is a side view of a building block;

FIG. 7 is a rear view of a building block; and,

FIG. 8 is a front view of a building block.

The broken line portions of the drawings are included to show portions of the building block that form no part of the claimed design. 

CLAIM The ornamental design for a building block, as shown and described. 